Anomalous kinetics of plasmas in high-power radiation fields

Transport equations are obtained in the nine-moment approximation for plasmas in intense radiation fields where the amplitude of the electron oscillations in the electromagnetic field exceeds the thermal speed. It is shown that for plasmas with a high degree of ionization, Z, the electron thermal conductivity is higher by approximately a factor of Z. The change in the frictional force on electrons colliding with ions owing to the effect of the radiation field leads to the possibility of electron acceleration and to a change in the sign of the dc and low-frequency electrical conductivities. Zh. éksp. Teor. Fiz. 111, 478–495 (February 1997)     

Renormalization of the Lorentz-Abraham-Dirac equation for radiation reaction force in classical electrodynamics

Dirac’s analysis of radiation reaction force in classical electrodynamics suggested that a 4-momentum not collinear with 4-velocity could be introduced for a radiating electron. This would be equivalent to renormalization of the electron mass as an operator relating these 4-vectors. Dirac also pointed to an arbitrary choice made in deriving the Lorentz-Abraham-Dirac (LAD) equation. It was shown that renormalization substantially modifies the LAD equation under the additional requirement that the standard relativistic relation ℰ² = p ² c ² + m ² c ⁴ holds for the renormalized energy and momentum. The renormalized LAD equation is more rigorous than the LAD equation, because the drawbacks of the latter are eliminated, and is simpler than a well-known approximation of the LAD equation. The renormalized LAD equation appears to be better suited for numerical simulations of processes in ultrahigh-intensity laser-pulse fields.     

Transition radiation of a charge in media with a nonuniform potential

The influence of a potential barrier on the transition radiation in the form of volume and surface electromagnetic waves emitted by a charged particle crossing an interface between media is investigated. It is shown that the volume-wave radiation field arises not only as a result of the jump in the dielectric constant at the boundary but also as a result of the velocity jump and the reflection of an electron induced by the presence of a nonuniform potential barrier. The angular distribution of the transition radiation intensity is obtained. Zh. Tekh. Fiz. 68, 11–14 (January 1998)     

Effect of an electron beam generated in an X-pinch plasma on the structure of the K spectra of multiply charged ions

The first experimental studies of an electron beam generated in an X pinch on the XP machine (Cornell University, USA) and the BIN machine (P. N. Lebedev Physical Institute, Russian Academy of Sciences) are reported. It is shown that it is possible in an X pinch to isolate the effect of a plasma-generated electron beam on the multiply charged ion radiation. The intensities of the satellite lines corresponding to Li-, Be-, B-, and C-like ions are calculated for the Al spectrum on the basis of a collisional-radiative model with a non-Maxwellian electron distribution in the plasma. The effect of an electron beam on the multiply charged light ion radiation in an X-pinch plasma is demonstrated. Comparing our calculations with the experimental spectra, we conclude that the present model can be used to estimate the electron beam intensity. Zh. éksp. Teor. Fiz. 112, 894–909 (September 1997)     

Resonant influence of hypersound on the radiation of an axially channeled electron

Abstract

The spectral intensity of the radiation emitted by an axially channeled electron in a single crystal excited by a longitudinal hypersonic wave propagating along the channeling direction has been calculated for the energy range 10MeV ≤ E ≤ 100 MeV. It has been shown that under the influence of acoustic vibrations excited in the single crystal a resonant intensification of the electron channeling radiation, a variation of its spectral distribution as well as inverse radiative transitions are possible.     

Excited hydrogenic atom in a strong low-frequency electromagnetic field

The multiphoton ionization of a bound electron state which is twofold degenerate with respect to its orbital angular momentum is considered in a quasiclassical approximation. It is shown that the ionization probability increases strongly in an intense electromagnetic field, in which nonresonant mixing of the levels forming the degenerate state is significant, in comparison to the case described by the Keldysh formula. It is also shown that such degeneracy leads to a sharp increase in the intensity of the radiation scattered by the bound electron, and the high-frequency cutoff of the emission spectrum is shifted to higher frequencies. Zh. Tekh. Fiz. 69, 15–20 (August 1999)     

Neutron radiation on tin anodes of lithium-ion batteries

Abstract

The operating durability of lithium-ion batteries is a principal problem in universe exploration or rescuing work in the nuclear radiation area. In the study, the neutron irradiation experiments were conducted on film-tin electrodes using the radiation dose of 10¹¹, 10¹², 10¹³ and 10¹⁴?n?cm^?2, respectively. The results show that the particle size grows with the increasing radiation does by atomic force microscopy (AFM) and scanning electron microscope (SEM). In addition, the degressive trend of specific capacity of tin anodes after neutron radiations increases with the increasing radiation dose. The fade of electrochemical performances may be attributed to the increasing particle size and defects induced by neutron radiation.     

Calculation of the interaction force between a relativistic electron beam and an Ohmic plasma channel

A formula for calculating the interaction force between a relativistic electron beam and a preformed Ohmic plasma channel with an arbitrary offset of the channel axis from the beam axis is obtained in the case of complete charge neutralization. It is shown that this force is repulsive for radial profiles of the conductivity with a peak on the channel axis. Zh. Tekh. Fiz. 67, 69–76 (June 1997)     

Mixing of bound states with electron transport by a radiation field in waveguides

Electron transmission in the two-, three-, and four-terminal nanostructures is considered under the influence of a radiation field. The frequency of the radiation field is tuned to the transition between the energy of a bound state and the Fermi energy of the incident electrons. The radiation induced resonant peaks and dips of the electron transport are exhibited for zero and low magnetic fields. It is shown that rotation of the radiation field polarization can effectively control the electron transport into different electrodes attached to the structures because of the symmetry of the structures. The resonant anomalies of the Hall resistance are found in a weak magnetic field. Zh. éksp. Teor. Fiz. 114, 1954–1970 (December 1998) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Radiative damping of a relativistic electron in classical electrodynamics

An exact solution of the problem of the reaction of the field generated by a relativistic classical electron is derived. It is found that the solution differs dramatically from the known formulas by the presence of a component that is even under time reversal. It is also shown that the component of the generalized radiative damping force that is odd under time reversal coincides with the well-known relativistic damping force obtained from the approximate nonrelativistic formula via a Lorentz transformation. Zh. éksp. Teor. Fiz. 114, 1661–1671 (November 1998)     

Anisotropic momentum transfer in low-dimensional electron systems in a magnetic field

In low-dimensional systems with an asymmetric quantizing potential, an asymmetric electron energy spectrum ε(p)≠ε(−p), where p is the electron momentum, arises in the presence of a magnetic field. A consequence of such an energy spectrum is that momentum transfer to the electron system in mutually opposite directions in the presence of an external perturbation is different. Therefore, in the presence of a standing electromagnetic wave momentum is transferred from the wave to the electrons, which gives rise to a new type of electromotive force. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 8, 551–555 (25 October 1997)     

Derivation of the vacuum longitudinal fieldB (3) from the Dirac equation of the electron in the electromagnetic field

By solving the Diras equation for the motion of an electron (c) in the circularly polarized electromagnetic field it is shown that the intrinsic electron spin forms an interaction Hamiltonian with a time independent fieldB ⁽³⁾ of electromagnetic radiation in the vacuum. In the same way as intrinsic spin is a fundamental property of the electron,B ⁽³⁾ is therefore a fundamental and intrinsic property of the vacuum electromagnetic field.     

Conductivity of ionic crystals when they are irradiated by picosecond electron beams

This paper discusses the pulsed electron conductivity σ of KCl, KBr, and NaCl crystals when they are excited by an electron beam (0.2 MeV, 50 ps) with current densities in the interval j=(30–10⁴) A/cm². It is shown that the lifetime of the electrons in the conduction band is τ≪100 ps. To explain the experimental σ(j) dependences, a model is proposed that includes electron capture by structural defects and stable radiation defects at low excitation densities and electron capture predominantly by unstable radiation defects generated by the excitation pulse at high excitation densities. Fiz. Tverd. Tela (St. Petersburg) 41, 1200–1203 (July 1999)     

On harmonic generation in a photoionized gas

The laws characterizing the radiation of high harmonics due to the coherent bremsstrahlung effect are indicated in the limit of high intensity of the laser pump photoionizing a gas in regime of suppression of the ionization barrier. It is shown that the intensity of the harmonics is determined by the quantum properties of the electron distribution in an atom before it is ionized. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 7, 486–490 (10 April 1999)     

Electron kinetics in a discharge plasma produced by a focused microwave beam in free space

A study is made of the electron kinetics in a discharge plasma produced by a high-power beam of electromagnetic radiation in the centimeter-wave region under conditions approaching free space, when the dimensions of the chamber are much greater than the wavelength of the microwave radiation. Two regimes of discharge production are investigated: the regime of short microsecond pulses at a repetition rate of 200 Hz, and a single millisecond pulse regime. It is shown that at threshold values of the microwave energy flux density the electron density in the initial stages of discharge formation reaches the critical value, and that the average energy of the electrons is of the order of 1.5–3 eV. Zh. Tekh. Fiz. 67, 10–14 (June 1997)     

Interaction of radiation and a relativistic electron in motion in a constant magnetic field

This paper examines the effect of multiple photon emission on the quantum mechanical state of an electron emitting synchrotron radiation and on the intensity of that radiation. Calculations are done with a variant of perturbation theory based on the use of extended coherent states. A general formula is derived for the number of emitted photons, which allows taking into account their mutual interaction. A model problem is used to demonstrate the absence of the infrared catastrophe in the modified perturbation theory. Finally, the electron density matrix is calculated, and the analysis of this matrix makes it possible to conclude that the degree of the electron’s spatial localization increases with the passage of time if the electron is being accelerated. Zh. éksp. Teor. Fiz. 113, 841–864 (March 1998)     

Nonlinear theory of channeling of radiation by a ribbon-shaped stream of cyclotron oscillators

The features of the nonlinear stage of radiation from transversely bounded, magnetically steered helical and rectilinear electron streams in a homogeneous medium and in vacuum are investigated theoretically under conditions of the normal and anomalous Doppler effects. The evolution of the transverse distribution of the radiated field is investigated, and the channeling effect of the electron stream is demonstrated. It is shown that in the radiation from a helical stream in a plasmalike medium a practically complete conversion of the energy of gyrational motion of the electrons into energy of electromagnetic oscillations can occur on account of the automatic fine tuning of the radiation angle. Zh. Tekh. Fiz. 69, 9–14 (January 1999)     

Relativistic ponderomotive forces

The interaction of a relativistic classical electron with an inhomogeneous electromagnetic field is investigated. In second-order perturbation theory the motion is separated into fast and slow motions, and the relativistic Newtonian equation is averaged over the fast oscillations. The rate of change obtained for the slow component of the electron momentum is interpreted as a relativistic ponderomotive force. The result is generalized to the relativistic case of the wellknown expression for the Gaponov-Miller force acting on an electron at rest. The expressions obtained for the relativistic ponderomotive forces are very complicated in the general case. They simplify in the limit of a stationary field (pulses of long duration) and a small gradient. The most typical and simplest special case of an inhomogeneous field—a stationary plane-focused beam—is investigated. The main difference between relativistic ponderomotive forces and their nonrelativistic limit is they have multiple components. In addition to the usual force directed along the gradient of the field, the relativistic case is also characterized by force components that do not have the form of the gradient of a potential and are parallel to the wave vector and the direction of the field polarization. It is shown that when a relativistic electron travels in a direction close to the direction of the wave vector of a focused laser beam, these components can greatly exceed the gradient force. A force directed along the field polarization vector arises even when the gradient of the field in this direction is zero. Zh. éksp. Teor. Fiz. 116, 1198–1209 (October 1999)     

Theory of group synchronism in free-electron waveguide lasers fed a sequence of short electron pulses

A theory of free-electron lasers fed a sequence of short electron pulses is developed. It is assumed that the group velocity of the electromagnetic pulse that develops in the cavity is the same as the translational velocity of the particles, and the repetition period of the electron pulses equals the transit time of the electromagnetic radiation in the cavity. Under these conditions of group synchronism, the principal factors governing the feasibility of establishing a stationary pulsed lasing regime are found to be the dispersive spread of the electromagnetic pulse and the channeling properties of an electron bunch. The conditions for self-excitation are found, and the characteristics of the stationary lasing regimes are determined assuming that the cavity has a high Q and using a parabolic equation for the evolution of the electromagnetic pulse shape. Zh. Tekh. Fiz. 69, 78–83 (February 1999)